Hello all,
I'm in the process of testing my Synthmonger CMOS resonant VCF into my Lunetta. The VCF thread is here and particularly the schematic is here.

The CMOS VCF needs to be run at 12v. The majority of the rest of my Lunetta runs at 5v. When I run outputs from a 40106 oscillator running at 5v into the VCF's audio input, the filter is working but very quiet. Even with the gain pot of the VCF at full, I loose a lot of signal between in and out. My guess is that this is caused by the mismatch in voltages and that increasing the gain of the input amplifier should fix it. Assuming that makes sense, looking at the schematic, is the 220K resistor between pin 12 and 13 of the 4069 what I need to change? If so, do I want to try a 2.2M for example?

I hate to see no replies to a question so I'll take a shot at this. Did you increase the feedback resistor and if so did it make a difference?
If you're just trying to run 5V logic level signals into the filter why not add a 4504 level shifter before the filter? This can convert 5V logic levels to 12V.

Sorry that this won't help with the original question, but thanks Brock for alerting me to the 4504 (I'd not heard of it before). Presumably this could be used to interface TTL-based Lunetta circuits to CMOS ones. I have seen some TTL designs which use chips that do not seem to have obvious CMOS analogues (or analogs). I might invest in a few just in case I find a good use for them.

The 4504 was developed to interface 4000 series cmos with TTL. The 74HC series cmos is more or less the logic equivalent of TTL but also includes a lot of 4000 series functions. Maximum voltage is 6V, typical 5V, and that's what I run all my Lunetta stuff at so I can use both series.

There are a bunch of ways to shift the levels. I'd probably build a little opamp amplifier. Both MFOS and CGS have some guitar pre-amp type circuits that you could steal. Or you could build a little comparator. Sounds like both might be useful in your system.

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